1. Field of the Invention
The present invention relates generally to a technique for oxidizing or reducing the surface of a work to be processed, removing or cleaning organic or inorganic substances and performing various surface treatments, and more particularly to a method and an apparatus for applying surface treatment to the surfaces of semiconductor devices, such as IC's, circuit boards and liquid crystal substrates, and circuits and electrodes formed on these surfaces.
2. Related Background Art
Heretofore, a variety of surface treatment techniques have been employed in the field for manufacturing semiconductor devices. For example, in a case where organic substances, such as a residue from soldering flux, are removed, a wet cleaning method using an organic solvent or a dry cleaning method, in which the organic substances are irradiated with ozone or ultraviolet rays to cause chemical reactions to take place so as to remove the organic substances, has been employed. If the wet cleaning method is employed, there is a risk that the electronic elements may be damaged. With the dry cleaning method, the ability to remove organic substances having large molecular weights is too poor to expect a satisfactory cleaning effect. Accordingly, a method has been developed recently in which gas discharge plasma, generated in a vacuum, is used to perform the surface treatment.
For example, in Japanese Patent Laid-Open No. 58-147143, there is disclosed a method that comprises the steps of using oxygen gas activated by microwave discharge performed in a reduced pressure environment to treat the surface of a lead frame so as to improve the hermetic contact of the leads with resin.
In Japanese Patent Laid-Open No. 4-116837, a method is disclosed in which 1 to 10 Torr of hydrogen gas is introduced into a plasma etching apparatus, and discharge is performed so as to cause reduction and remove oxides.
In Japanese Patent Laid-Open No. 5-160170, there is disclosed a method in which high-frequency voltage is applied to an electrode in a reduced pressure processing chamber, to generate argon-oxygen oxidizing plasma or hydrogen reducing plasma to etch a lead frame.
However, in the case where plasma discharge takes place in a vacuum or in a reduced pressure environment, special equipment, such as a vacuum chamber and a vacuum pump are required. Thus, the overall size of the apparatus is enlarged and the structure of the apparatus is unnecessarily complex. Therefore, the cost of the apparatus as well as the cost of performing the method cannot be reduced. What is worse, the pressure in the chamber must be reduced and maintained for the entire time of performing the discharge. Therefore, the time it takes to complete the process is also lengthened.
Since the processing performance is unsatisfactory and the operation cannot easily be completed in a short time, the manufacturing yield deteriorates. Moreover, the plasma discharge in a vacuum or in a reduced pressure environment, raises the risk of thermal or electrical damage because large quantities of electrons and ions are present with respect to activated, or high energy gas molecules. As a result, portions of the work to be processed may be damaged or affected adversely.
On the other hand, methods have been disclosed in recent years, each method including the step of using noble gas and a small quantity of reaction gas to generate plasma at or about atmospheric pressure to perform a variety of surface treatments, such as ashing and etching. The foregoing methods usually include the step of causing discharge to take place directly between a high-frequency electrode and a work to be processed. For example, in Japanese Patent Laid-Open No. 4-334543, a method has been disclosed in which plasma is generated in a pipe to process the inner surface of the pipe and substances passing through the pipe. Furthermore, a method is known that employs a surface treatment apparatus disclosed in Japanese Patent Laid-Open No. 3-219082, in which discharge takes place between a power-source electrode and a grounded electrode, and the plasma produced by discharge is sprayed to the surface of a work to be processed, optionally to form a desired film from the activated gas.
In recent years, to meet the desire for improving the performance and reducing the size of semiconductor apparatuses, IC elements and circuit boards of a type using multi-layer circuits have been used widely. In a case where a multi-layer circuit is formed on a substrate, initially traditional photo-lithography techniques are used to form a metal circuit made of conductive metal, such as aluminum or the like, on the substrate by patterning, followed by being covered with an insulating film made of SiO.sub.2 or the like. The second metal circuit layer is formed on the insulating film, by etching a pattern into an applied metal film similarly by the conventional photo-lithographic technique so that a desired circuit pattern is formed. However, since a pin hole can easily be formed in the SiO.sub.2 insulating film, patterning of the second metal circuit layer formed on the SiO.sub.2 film raises a risk that the first or lower metal circuit formed under the SiO.sub.2 insulating film will be undesirably etched and thereby damaged. Accordingly, a method has been employed in which the SiO.sub.2 insulating film is made to be excessively thickened to avoid pinholes, or like imperfections. However, a long time and great labor are required to form the SiO.sub.2 insulating film of excessive thickness, thus resulting in the cost being raised, time lengthened and the manufacturing yield severely deteriorated. Furthermore, the semiconductor device is thickened more than necessary, and therefore the desire for reducing the size and the thickness of the substrate and the electronic elements cannot be met.
Liquid crystal devices (LCD) usually comprise a glass substrate using a transparent electrode made of Indium-Titanium-Oxide (ITO) or the like. In a particular case of a liquid crystal device for use in a word processor or a personal computer screen, since a relatively large electric current flows when it is operated, the transparent electrode must have as weak a circuit resistance as possible. Accordingly, a method has been employed in which the thickness of the transparent electrode is increased. However, since the transparent electrode is usually formed by a vacuum film-forming method, a long time is required to form the same at the desired thickness, and therefore the cost cannot be reduced. Furthermore, the transparency deteriorates in proportion to the thickness of the transparent electrode, thus adversely affecting the function of the liquid crystal display.
To overcome the foregoing problems, the inventors of the present invention paid attention to the fact that previous coating of the surface of the lower metal circuit with an oxide is useful to protect the lower metal circuit from being etched at the time of patterning the upper metal circuit, even if the SiO.sub.2 film formed on the lower metal circuit has pin holes or other imperfections. Furthermore, coating of the surface of a metal circuit or an electrode that appears on the surface of the substrate with a metal oxide enables the surface to have corrosion resistance against a variety of contamination factors. As a result, the reliability of the circuit and the like can be improved and the lifetime of the same can be lengthened.
Furthermore, the inventors of the present invention paid attention to a fact that reduction and metallizing of a transparent electrode enables a desired low resistance to be realized without the necessity of excessively thickening the transparent electrode when the electrode is made of a metal oxide. However, in any case, the foregoing surface treatment techniques encounter a variety of difficulties in practical use.
When a liquid crystal display apparatus is manufactured in the conventional manner, an oriented film has been formed on the surface of a liquid crystal panel by a method including the steps of forming a heat-resisting synthetic resin coating film having an electrical insulating characteristic and made of, for example, polyimide, on the substrate; and rubbing the surface of that coating film in one direction with a roller around which a cloth is wound. The substrate and resin coating are subjected to a rubbing process, so that the film is oriented. However, the foregoing method in which the surface is physically rubbed raises a problem in that the synthetic resin coating film may be separated from the substrate, and dust or the like allowed to adhere to the cloth wound around the roller or the surface of the coating film damages the surface of the coating film. Although the orientation must be realized uniformly, the conventional methods produce results that vary considerably. In addition, the angles and the inclinations scatter considerably, and the surface subjected to the rubbing process cannot be evaluated easily for determining when the rubbing process has been completed. In addition, the angle of the oriented film cannot be easily controlled except by trial and error of an experienced operator.